In a semiconductor manufacturing process, film formation on a semiconductor wafer using plasma, etching and so on are performed. Japanese Patent No. 5204476. and Japanese Patent No. 5595136 each disclose an inductively coupled plasma (ICP) generation device. The plasma generating device is provided with an antenna coil that is wound around a cylindrical vacuum chamber, a high-frequency power source that applies high-frequency voltage to the antenna coil and a matching device that performs impedance matching between the antenna coil and the high-frequency power source. The matching device is a circuit configured to include a coil and a variable capacitor connected in a series-parallel manner.
FIG. 3 is a circuit diagram of an example of the configuration of a conventional plasma generating device.
A high-frequency power source 3 includes a DC power source 30 that outputs direct current (DC) voltage and a full-bridge inverter circuit 31 that converts the DC voltage output from the DC power source 30 into high-frequency voltage with frequencies of high frequency bands (approximately 1-3 MHz, for example) and that outputs the converted voltage. The full-bridge inverter circuit 31 is constructed by first to fourth switching elements 31a, 31b, 31c and 31d. Note that the sources of the second and fourth switching elements 31b and 31d are connected to a reference potential, for example, a container of the plasma generating device.
Switching on or off of the first to fourth switching elements 31a, 31b, 31c and 31d is controlled by a control unit (not illustrated). The control unit alternately switches between a conductive state in which the first and the fourth switching elements 31a and 31d are turned on and a conductive state in which the second and the third switching elements 31b and 31c are turned on to thereby enable output of high-frequency voltage from the full-bridge inverter circuit 31.
Note that a contact point between the source of the first switching element 31a and the drain of the second switching element 31b is assumed as a first output terminal portion 32 while a contact point between the source of the third switching element 31c and the drain of the fourth switching element 31d is assumed as a second output terminal portion 33.
A resonance circuit 4′ is provided with a first series reactance element 41 connected in series between one end portion 21a of an antenna coil 21 and the first output terminal portion 32 of the high-frequency power source 3. The resonance circuit 4′ is further provided with a parallel reactance element 43 connected in parallel with the antenna coil 21.
Moreover, the one end portion 21a of the antenna coil 21 is positioned at an inlet 11 side of the vacuum chamber 1 while the other end portion 21b of the antenna coil 21 is positioned at an outlet side of the vacuum chamber 1.